1. Field of the Invention
The present invention relates to a liquid discharge head which discharges liquid droplets as fine liquid droplets, and specifically, to a liquid discharge head suitably used as an inhalation device which is used when a solution including a medicine in a medical field is inhaled into the lungs in the form of mist.
2. Description of the Related Art
Conventionally, a liquid discharge head which discharges a liquid as fine liquid droplets is widely used as an ink jet head in a recording field. Not only is the discharging of liquid droplets but also the controllability of the discharge direction of liquid droplets is required in the ink jet head. In a conventional ink jet head, various proposals for satisfying these requests have been made. For example, Japanese Patent Application Laid-Open No. 2004-001439 discloses an ink jet recording head which discharges liquid droplets from nozzles, which are located at least at ends of a plurality of nozzles arrayed in one direction, in an oblique direction to a discharge surface. The inclining of the nozzles solves the problem that the pitch of joining portions becomes wide, and a gap is formed at a landing position on a sheet when a plurality of these heads is joined together. As methods of discharging liquid droplets obliquely, a formation where there is a height difference in the depth direction of nozzles and a method of performing hydrophilic treatment and water-repellent treatment on the inner wall surfaces of the nozzles asymmetrically have been disclosed. Additionally, Japanese Patent Application Laid-Open No. 2001-105584 discloses a method of arranging at least two energy generating elements at one discharge port to control the driving thereof, thereby changing the discharge directions of liquid droplets at random to solve the concentration unevenness in printing. Discharging ink obliquely in an ink jet recording field in this way has various merits.
However, in a conventional ink jet head in the ink jet recording field, how precise and dense printing dots are filled in high density on a target sheet is the main point of the improvement in the quality of an image. Therefore, energy generating elements are arrayed as densely as possible, one discharge port is arranged for each energy generating element, and discharge ports through which discharge is made according to a driving signal for each energy generating element are made to be as many as possible. This allows compatibility between high resolution and faster printing. Additionally, if the printing dots are dense, resolution improves to a certain degree. However the printing dots may be made dense to such an extent that a person can recognize visually, and it is sufficient if the diameter of discharge ports are reduced to about 10 μm at the utmost.
The aforementioned Japanese Patent Application Laid-Open No. 2004-001439 and Japanese Patent Application Laid-Open No. 2001-105584 have also been devised under the background of the technical fields thereof.
However, in the liquid discharge head used for an inhalation device which is used when a liquid medicine in a medical field is inhaled into the lungs in the form of mist, the discharged droplet diameter is about several micrometers, and optimally, about 2 μm to about 6 μm. Therefore, about 1 to 5 μm is required for the diameter of the discharge ports, and significantly smaller discharge ports are required compared to the discharge ports of the conventional liquid discharge head used in the ink jet recording field. Additionally, in order to shorten inhalation time to relieve burden on a patient, it is necessary to discharge a large amount of liquid droplets in order to prescribe the amount of medicinal solution required in a shortest time possible.
In a case where the amount of discharge per unit time is the same, when the discharged droplet diameter is 3 μm, the same total amount of discharge is not obtained if the number of liquid droplets is not about 40 times the number of liquid droplets compared to the discharged droplet diameter of 10 μm. Due to this, the focal point is how the number of discharged liquid droplets is increased in the liquid discharge head which is used when a liquid medicine in a medical field is inhaled into the lungs in the form of mist compared to the conventional liquid discharge head which is used in the ink jet recording field.
Discharging large amount of liquid droplets in a short time is allowed simply if energy generating elements are increased or discharge ports are increased. However, a discharge head is enlarged, and accordingly, a driving battery also becomes large. Then, as well as the inhalation device becoming enlarged, and the convenience for a patient deteriorating, the cost of an enlarged head becomes high. In order to solve these problems, it is possible to make the interval between discharge ports as narrow as possible to arrange as many discharge ports as possible on an energy generating element as in Japanese Patent Application Laid-Open No. 2003-154655.
However, when the interval between adjacent discharge ports is made to be narrow, a problem has occurred in that discharged liquid droplets come into contact and join up with each other, which produce large liquid droplets, and required optimal liquid droplets cannot be obtained.
In case of the liquid discharge head used for an inhalation device which is used when a liquid medicine in a medical field is inhaled into the lungs in the form of mist, it is necessary to obtain the largest therapeutic effect with as small an amount of a medicinal solution as possible in consideration of physical and economic burdens on the patient. For that purpose, a discharged liquid droplet group needs to include only liquid droplets of an optimal diameter in portions where the liquid droplets are required to reach. This is because, if the diameter of a discharged droplet is greater than the optimal diameter, the droplet may adhere into the inside of the mouth or the bronchus before reaching the lungs, and if the diameter is smaller than the optimal diameter, the droplet may be discharged to the outside of a body during exhalation even when the droplet has reached the lungs.
As mentioned above, in the liquid discharge head used for an inhalation device which is used when a liquid medicine in a medical field is inhaled into the lungs in the form of mist, the diameter of discharge ports is required to be about 1 to 5 μm. These discharge ports are significantly small discharge ports compared to the discharge ports of the conventional liquid discharge head used in the ink jet recording field. Therefore, when a discharge port portion is machined in the shape as described in Japanese Patent Application Laid-Open No. 2004-001439 as the method of inclining the discharge directions in order to prevent liquid droplets discharged from adjacent discharge port from coming into contact and joining up with each other, removal of machining scraps is difficult. When discharge ports are formed not by machining but by photolithography, development scum will remain during exposure and development. Machining of fine holes is difficult by any discharge port operation method. Additionally, in the case of fine holes, the method of dividing the surface property of the inner wall of a discharge port into a hydrophilic property and a water-repellent property by coating is not possible in practice, and is not practical because substantial time and effort are required.